1. Field of the Invention
The invention relates to industrial furnaces, particularly a cooled jacket for electric arc furnaces.
2. Description of the Prior Art
Electric arc furnaces are in general use for the production of special steels. The body of the furnace mainly consists of a cylindrical casing, a convex base forming a furnace shell and a convex cover. The casing includes a feed aperture and a pouring aperture fitted with a spout and usually provided on the opposite side to the aperture, while the cover includes the apertures required for the electrodes. The body of the furnace is mounted on rollers and can be emptied by tilting it. The internal walls of the furnace have a more or less thick refractory lining serving to absorb the considerable heat to which they are exposed.
It has been found that with the very high temperatures which naturally occur in these arc furnaces the side casing, which consists of a metal armoring with a refractory lining, is only just capable of standing up to the high thermal stresses to which it is subjected. The metal armoring is liable to bulge outwards and the lining only has a life of 80-100 charges, i.e. operating cycles, and therefore the armoring has to be renewed frequently. This renewal of the lining involves considerable expense, as well as a reduction in output, as a result of the temporary stoppage thereby caused.
The policy has therefore been adopted of equipping the side of the furnace with a cooling system by integrating cooling boxes into this wall on similar lines to those already known in connection with the operation of blast furnaces. These cooling boxes or cooling elements for arc furnaces can be designed as integral supporting parts of the side of the furnace and arranged in such a manner that a plurality of mutually adjacent cooling elements, preferably curved in the form of a circle, form a belt which in this zone constitutes the side of the furnace. This belt-shaped configuration of cooling elements may be provided on the inside and if necessary on the outside likewise with a refractory coating.
The cooling elements themselves consist of flat curved hollow boxes of about 200-250 mm in thickness, with a water inlet usually provided at the top and a water outlet situated at the bottom. The cooling water passing through the system is caused to flow along a serpentine path by means of horizontal crosspieces provided in mutually offset positions inside the cooling boxes to form baffle-shaped flow channels. It is true that the use of these cooling boxes has enabled the life of the furnace jacket to be considerably increased, but the constructional principle of this cooling system suffers from a number of serious drawbacks.
For technological reasons it is only at certain isolated points on their narrow sides that the aforementioned crosspieces are welded to the housing of the cooling elements. More or less wide gaps are thus left between the narrow sides of the crosspieces and the outer walls of the housing, giving rise to considerable vagabond currents of water and thus detracting from the cooling effect and increasing the water consumption.
Furthermore, the material, particularly the welds of the elements, are subjected by the considerable heat gradient between their sides nearest to the furnace and their outer sides to heavy stresses and to the corresponding latent risk of faults. In addition, these cooling elements, owing to their geometric construction, involving flat boundary walls of large area, with the attendant risk of deformation, are unsuitable for operation where comparatively high water pressures occur, so that their cooling efficiency remains relatively limited. The interior of these cooling boxes also includes numerous blind angles, particularly in the zone where the water is guided around the free ends of the crosspieces, increasing the risk of eddies and steam bubbles and the resulting local heat accumulation and greater resistance to flow. The higher manufacturing costs are a further disadvantage of these known cooling boxes.